This invention provides improved air conditioning systems particularly useful in large passenger aircraft. However, it will be recognized that the concept has other applications as well and that the preferred form in which it is herein illustratively described is subject ot modifications and changes without departing from the essentials of the invention itself.
It has become largely conventional in modern passenger aircraft to satisfy cabin ventilation requirements with cooled outside air delivered under pressure and at a rate at least twice that required to maintain cabin pressure. As a result, normal operation of the cabin pressure control system results in dumping into the atmosphere at least as much air as that which leaks out through the joints and seals during high elevation flight. Fans and ducting within the cabin distribute the air in such a way as to maintain uniformity of temperature and ventilation in all required areas of the cabin.
In that type of system, the outside air supply was provided by bleed air from the engine compressor stages and was fed through heat exchangers and an air cycle machine (ACM) to reduce its temperature pressure and through a coalescer bag-type water separator to remove water. The system has shortcomings. Energy, hence fuel, required to produce this added increment of compressor bleed air output is high and it is expensive (approximately 6% of inflight fuel comsumption). Also, the coalescer bag-type water separator presents maintenance problems due to build-up of dust, oil droplets, and other particles in the bag interstices.
Attempts to maintain adequate ventilation with reduced engine bleed airflow rate compensated with recirulation air from the cabin by substantially reducing the temperature of ACM discharge air fed to the coalescer bag-type water separator would be met with the lower practical temperature limit of about 35.degree. F. to prevent clogging of the coalescer bag with ice. In order to maintain satisfactory cooling performance with the foregoing temperature limitation, increased engine bleed air output is required, which materially increases engine operating fuel cost.
A primary object of the present invention is to overcome the aforementioned problems and limitations, and more specifically to provide an air conditioning system for the purposes indicated which permits utilizing recirculated cabin air effectively, substantially eliminating the prior maintenance problem with coalescer bag-type water separators, and substantially reducing operating cost in fuel consumption while providing for the same degree of ventilating air movement into the aircraft cabin as heretofor.